We plan to study the physiological effects on mammals and birds of stresses, notably exercise and low oxygen (high altitude), on the respiratory, cardiovascular and thermoregulatory systems. Sustained levels of heavy exercise will be obtained by use of treadmills (mammals and birds) and flight in wind-tunnels (birds) and altitude will be simulated in a hypobaric chamber. We will study energy metabolism, respiratory parameters (ventilation, tidal volume, frequency), oxygen uptake in the lung, blood parameters (oxygen dissociation curves, A-V oxygen concentrations), circulation rates, oxygen delivery to exercising muscles (blood flow and A-V oxygen differences), heart function (frequency, stroke volume, cardiac output) and thermoregulation (heat production and balance, evaporation) during exercise and hypoxia.